Mercury: Element of the Ancients

The Promise of Power

Intriguing because of its silver hue and liquid state at room temperature, elemental mercury was known to the ancient Greeks, Romans, Chinese and Hindus. Each civilization had its own legends about mercury, and it was used as everything from a medicine to a talisman. Mercury's chemical symbol, Hg, comes from the Greek "hydrargyrum" meaning liquid silver. Mercury is also known as "quicksilver," a reference to its mobility. Speed and mobility were characteristics of the Roman god, Mercury, who served as a messenger to all the other gods and shared his name with the planet nearest the sun. The symbol for the planet was used by the alchemists to identify mercury before it was given its more modern chemical notation.

Although mercury's mystique held the promise of power, many of the ancients also knew it to be toxic. It was in the mining of the element where mercury first became associated with human illness beginning as tremors and progressing to severe mental derangement. The largest natural source of mercury is cinnabar, its only known ore, and the richest deposits are found in Spain and Italy. This reddish mineral containing mercury and sulfur has been used as a pigment since prehistoric times. Cinnabar dating from 500 BC has been identified at a Mayan site in Guatemala, and prehistoric skulls painted with cinnabar have been found in Italy.

The Romans used their mercury mines as penal institutions for criminals, slaves, and other undesirables. The warders were among the first to recognize that there was a high likelihood that the prisoners would become poisoned and spare the keepers the need for formal executions. Mercury is primarily a neurological poison, causing tremors, extreme mood changes, and eventually loss of hearing and restricted vision. Certain forms of mercury poisoning also cause damage to the liver and kidneys. The life span of a worker in those mines was tragically brief.

From Mercury to Gold?

In the ancient art of alchemy, mercury, sulfur, and salt were the Earth's three principle substances. The Hindu word for alchemy is "Rasasiddhi", meaning "knowledge of mercury." Believing that mercury was at the core of all metals, alchemists supposed that gold, silver, copper, tin, lead and iron were all mixtures of mercury and other substances. While alchemists in different cultures had different beliefs, one of the central themes to European alchemy was the belief that the correct combination of mercury and other ingredients would yield riches of gold.

The Roman emperor Diocletian (245-313) issued an edict in the late 3rd century calling for the destruction of all written works dealing with alchemy. Diocletian feared that artificially created gold would debase the value of the Roman currency and allow alchemists to amass huge fortunes with which they could bribe officials and gain power.

Chinese alchemist - Ko Hung

False Promises of Longevity and Health

The line between alchemy and medicine was not always clear. In 2nd century China, the study of mercury centered on a search for an elixir of life to confer longevity or immortality. The prominent Chinese alchemist Ko Hung, who lived in the 4th century, believed that man is what he eats, and so by eating gold he could attain perfection. Yet, he reasoned, a true believer was likely to be poor, and so it was necessary to find a substitute for the precious metal. This, in his estimation, could be accomplished by making gold from cinnabar. Ko Hung's other uses for cinnabar included smearing it on the feet to enable a person to walk on water, placing it over a doorway to ward off thieves, and combining it with raspberry juice to enable elderly men to beget children.

In the era before antibiotics, sexually-transmitted diseases were deadly. Some scholars believe that syphilis was the most critical medical problem of the first half of the 16th century. A great number of printed works dealing with syphilis first appeared at the end of the 15th century when it was known by such names as "morbus gallicius," "the French disease," "the pox," and "lues venera." In the desperate search for a cure, it was almost inevitable that various forms of mercury would be tried. Indeed, the treatment appeared to benefit some patients. While it is unclear whether mercury actually did cure syphilis (some cases of the disease resolve spontaneously), the use of mercury therapy continued into the early 20th century.

Mercury and Hatters

The felt hat industry has been traced to the mid-17th century in France, and it was probably introduced into England some time around 1830. A story passed down in the hat industry gives this account of how mercury came to be used in the process: In Turkey camel hair was used for felt material, and it was discovered that the felting process was speeded up if the fibers were moistened with camel urine. It is said that in France workmen used their own urine, but one particular workman seemed consistently to produce a superior felt. This person was being treated with a mercury compound for syphilis, and an association was made between mercury treatment of the fibers and an improved felt.

Danbury Hat Factory

Eventually the use of solutions of mercuric nitrate was widespread in the felt industry, and mercury poisoning became endemic. Danbury, Connecticut, an important center of America's hat-making industry until men's hats went out of fashion in the 1960s, developed its own reputation for madness. Regionally, the "Danbury shakes" were a commonly recognized series of ailments.

On December 1, 1941 the United States Public Health Service banned the use of mercury in the felt industry in this country. Although it has been suggested that the expression "mad as a hatter" and the character portrayed in Lewis Carroll's Alice in Wonderland may have other origins other than mercurialism among hatters, few can resist making this apocryphal analogy.

Mercury in the Aquatic Food Web

In nature mercury can be found in several forms. It can be converted from one form to another by natural processes. For example, when the elemental mercury released in emissions from coal-burning power plants or waste incinerators is deposited on lakes and streams it can be converted to inorganic mercury and then to organic forms by microorganisms. Some forms of mercury are particularly potent poisons.

In 1958 a unique illness began to be recognized in the area around Minamata Bay, on the Japanese island of Kyushu. Sixty-eight people died while 397 others exhibited neurological problems. The highest rate of illness was among fishermen and their families. It turned out that chemical industries around the bay had been discharging inorganic mercury wastes into the waters, where anaerobic bacteria in the detritus on the floor of the bay converted the inorganic mercury into methylmercury. The methylmercury became concentrated as it was passed along natural food webs. It found its way into fish and shellfish that were consumed by people living around the bay. Scientists estimated that biomagnification in food chains may have been as high as a millionfold.

Methylmercury produces a much more devastating human illness than inorganic mercury, affecting primarily the central nervous system with many neurologic disturbances including paralysis, "tunnel vision" and blindness. There is no effective antidote as there is for inorganic mercury salts, nor are there any truly efficacious means for hastening its excretion from the body. Unfortunately, methylmercury is also very dangerous to a developing fetus. Offspring exposed in utero, if they survive, may have an irreversible affliction resembling cerebral palsy. Experimentally, methylmercury has been shown to cause mutations in DNA as well.

Since the Japanese community lived on locally caught fish, the problem was limited to a relatively small area and population, and the problem came to light quickly. While the local people were exposed to high levels, the contamination was not widespread beyond this region. Japanese officials were reluctant to publicize this incident, however, which might have prevented the occurrence of other episodes in subsequent years. A very similar poisoning, leaving 13 dead and 330 affected, took place in 1965 around Niigata, Japan, on the island of Honshu.

There are a number of populations in the world that consume large amounts of mercury-contaminated fish, such as the indigenous populations of Cree and Inuit Native Americans living in the province of eastern Quebec, Canada. Some of these communities were displaced in a huge project to develop hydroelectric power. During the James Bay project by Hydro-Québec, the rerouting of rivers and massive flooding of previously dry lands mobilized environmental mercury that had always been in the soil. Bacterial action transformed some of that pool into methylmercury, which began to accumulate in natural food chains. Freshwater fish are a dietary staple for these native populations. The provincial government has instituted hair analysis programs to monitor exposure.

Methylmercury is also found in saltwater fish, again posing a dilemma to public health officials. The health benefits of even modest fish consumption are well known, particularly in the prevention of cardiovascular disease, so there is a delicate balance between achieving those benefits and the risk of too much mercury exposure. The Native American populations of Quebec consume fish primarily during the summer months, and the mercury content of their hair reflects peak concentrations during the summer and lower concentrations during the winter. In contrast, populations that depend on ocean fish as their main source of protein tend to have relatively stable elevated levels of mercury in their hair. Fortunately, limited studies in both types of consumers suggest that they are not exhibiting even the most subtle signs of poisoning.

Studies of wildlife have come to different conclusions, however. In Maine and New Hampshire there is evidence that loons have experienced reproductive and immune problems due to cumulative poisoning from eating mercury-contaminated fish.

A Mass Poisoning

In 1971-72, a major epidemic occurred in Iraq in which 6,530 persons were hospitalized and almost 500 died. In a well-intentioned humane response to famine, several nations shipped wheat grain intended for planting to Iraq. The seeds had been treated with a methylmercury-containing fungicide to hold down mold growth and preserve the viability of the seeds. The seeds were also dyed red to serve as a warning, and attempts were made to inform the natives of the hazards of eating the seeds directly. Unfortunately, the warnings on the bags were in Spanish, because some of the grain had originated in Mexico, and the skull and crossbones, recognized by westerners as meaning poison, meant nothing to the Iraqis. In the face of starvation many families milled the seeds directly into flour, and made and consumed the contaminated bread. There would have been no danger in eating grain grown from the treated seeds, because the subsequent crop would contain little or no methylmercury.

The population of the United States has been fortunate in avoiding mass poisonings in the past, but there was one isolated series of cases in 1970 involving a single family in Almagordo, New Mexico. The father worked in a seed store, which supplied local farmers, and he maintained a few pigs at home. He noticed a significant amount of wastage in the form of spilled seed grain at the store, and he began sweeping it up to feed to his pigs. Within a short time his pigs became obviously ill. Fearful of the loss of his investment, the father had them butchered, and he froze the meat for the use of his family. Three of them were eventually poisoned severely.

Twenty-two years after this incident all surviving members of the family were carefully examined and tested. In this interim the two youngest children had died, and autopsy and toxicological findings were available from one of these. Both were left in a vegetative state until their deaths. Some recovery did occur in the older children, but the visual defects, including blindness in one and constricted visual fields in the other, did not improve. Neither parent showed signs of poisoning, although both were exposed. Toxicological studies suggested that methylmercury, which readily crosses the blood-brain-barrier, is converted to inorganic mercury in the brain. Since inorganic mercury does not readily cross biological membranes, it is effectively trapped in the brain, but it is not clear which of the two species is responsible for the brain pathology.

The use of methylmercury as a fungicide has been suspended in the United States, and since this was the only commercial use for the chemical, it is no longer manufactured in this country. It is, however, still found in the environment as a result of bacterial methylation of inorganic mercury.

The Ubiquitous Thermometer

Throughout the 20th-century, mercury has been useful in a number of everyday items  alkaline batteries, fluorescent light bulbs, electrical switches, scientific and medical devices and the ubiquitous thermometer. Thermometers contain the less toxic elemental form of mercury and have almost never been a safety issue in peoples' homes. However, in the 1970s and '80s, workers at the Staco thermometer plant in Poultney, Vermont, began to notice a common series of health problemsheadaches, bleeding or sore gums, upset digestive systems, and coordination problems. Upon investigation, mercury was detected in the air of workers' homes, on their clothing and furniture, and most tragically, in the bodies of many workers and their children. This was the first time in which the children of mercury-handling workers were proven to have been affected. The plant closed in 1984. Several plant workers have since settled lawsuits with the company for undisclosed sums. Another lawsuit brought against the company by the town of Poultney and the state of Vermont was settled in September of 1991. Staco paid $289,000 to the town of Poultney for costs related to the clean-up of the town's water treatment plant.

As part of a goal to eliminate mercury from medical equipment, some communities have sponsored thermometer exchanges. For example, at a one-day event in 1999, the Dartmouth-Hitchcock Medical Center in Hanover, New Hampshire exchanged approximately 800 mercury thermometers brought in by staff for digital, non-mercury thermometers.

Mercury Tragedy at Dartmouth

Karen Wetterhahn, Ph.D.

Mercury caused a tragic incident in Hanover, New Hampshire, in 1997. The story of Dartmouth College Chemistry professor Karen E. Wetterhahn made national headlines when mercury poisoning claimed her life at the age of 48. Wetterhahn, a specialist in toxic metals, was poisoned in her lab by a few drops of the rare, extremely toxic compound dimethylmercury which accidentally penetrated her protective glove. Dimethylmercury, a colorless liquid, is a synthetic compound used almost exclusively as a reference standard in a particular type of specialized chemical analysis. Ironically, Wetterhahn was investigating the toxic properties of another metal, cadmium, and was merely using the dimethylmercury as a reference for her instrumentation when she was poisoned. While the accidental spill occurred in August of 1996, symptoms of her mercury poisoning were not detected until six months later, at which time the illness was irreversible. Wetterhahn became suddenly ill in January of 1997 and was hospitalized. She rapidly went into a coma and died that June. As a result of her tragedy, safety standards for gloves and other protective equipment were revised, and a movement began to eliminate production and use of this most deadly form of mercury.

Article by: Julie Sloane, Science Writer

Supported by the National Institute of Environmental Health Sciences Superfund Research Program